1. Technical Field
The present invention generally relates to polysiloxane prepolymers and their use as biomedical devices such as ophthalmic lenses.
2. Description of Related Art
In the field of biomedical devices such as contact lenses, various physical and chemical properties such as, for example, oxygen permeability, wettability, material strength and stability are but a few of the factors that must be carefully balanced in order to provide a useable contact lens. For example, since the cornea receives its oxygen supply exclusively from contact with the atmosphere, good oxygen permeability is a critical characteristic for any contact lens material. Wettability also is important in that, if the lens is not sufficiently wettable, it does not remain lubricated and therefore cannot be worn comfortably in the eye. Accordingly, the optimum contact lens would have at least both excellent oxygen permeability and excellent tear fluid wettability.
Hydrogels represent a desirable class of materials for many biomedical applications, including contact lenses and intraocular lenses. Hydrogels are hydrated, cross-linked polymeric systems that contain water in an equilibrium state. Silicone hydrogels are a known class of hydrogels and are characterized by the inclusion of a silicone-containing material. Typically, a silicone-containing monomer is copolymerized by free radical polymerization with a hydrophilic monomer, with either the silicone-containing monomer or the hydrophilic monomer functioning as a crosslinking agent (a crosslinker being defined as a monomer having multiple polymerizable functionalities) or a separate crosslinker may be employed. An advantage of silicone hydrogels over non-silicone hydrogels is that the silicone hydrogels typically have higher oxygen permeability due to the inclusion of the silicone-containing monomer. Because such hydrogels are based on monomers polymerizable by free radical, these materials are thermosetting polymers.
U.S. Pat. No. 5,034,461 discloses neutral polyurethane-containing prepolymers. These prepolymers may be copolymerized with a hydrophilic comonomer to form a silicone hydrogel copolymer that is useful as a contact lens material and other biomedical device applications. The prepolymers exemplified in U.S. Pat. No. 5,034,461 do not include any major hydrophilic portion, and therefore, these prepolymers are copolymerized with a hydrophilic monomer to form a hydrogel copolymer.
It would be desirable to provide improved biomedical devices formed from silicone-containing material that exhibit suitable physical and chemical properties, e.g., oxygen permeability and wettability, for prolonged contact with the body while also being biocompatible.